Thermal interface structure with integrated liquid cooling and methods

ABSTRACT

A method and device for thermal conduction is provided. A thermal interface device and method of formation is described that includes advantages such as improved interfacial strength, and improved interfacial contact. Embodiments of thermal conduction structures are shown that provide composite thermal conduction and circulated liquid cooling. Embodiments are further shown that require simple, low numbers of manufacturing steps and reduced thermal interface thickness.

TECHNICAL FIELD

The present invention relates generally to the field of heat transferand, in particular, the present invention relates to thermal managementof electronic devices.

BACKGROUND

In one embodiment, the present invention is used to transfer heatgenerated by electronic devices or groups of devices, such astransistors, as are commonly included on integrated circuit (IC) chipssuch as processor chips.

In the field of electronic systems there is an incessant competitivepressure among manufacturers to drive the performance of their equipmentup while driving down production costs. This is particularly trueregarding forming electronic devices such as transistors in IC's, whereeach new generation of IC must provide increased performance,particularly in terms of an increased number of devices and higher clockfrequencies, while generally being smaller or more compact in size. Asthe density and clock frequency of IC's increase, they accordinglygenerate a greater amount of heat. However, the performance andreliability of IC's are known to diminish as the temperature to whichthey are subjected increases, so it becomes increasingly important toadequately dissipate heat from IC environments.

With the advent of high performance IC's and their associated packages,electronic devices have required more innovative thermal management todissipate heat. Increasing speed and power in processors, for example,generally carry with it a “cost” of increased heat in themicroelectronic die that must be dissipated. What is needed is a deviceand method to more effectively cool microelectronic dies containing IC'ssuch as processors. What is also needed is a device and method that isless expensive and easier to manufacture.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an information handling device according to oneembodiment of the invention.

FIG. 2A illustrates a side view of a processor assembly according to oneembodiment of the invention.

FIG. 2B illustrates an isometric view of a processor assembly accordingto one embodiment of the invention.

FIG. 3A illustrates a side view of an integrated circuit assemblyaccording to one embodiment of the invention.

FIG. 3B illustrates a side view of an integrated circuit assemblyaccording to one embodiment of the invention.

FIG. 3C illustrates a side view of a processor assembly according to oneembodiment of the invention.

FIG. 4 illustrates a top view of an integrated circuit assemblyaccording to one embodiment of the invention.

FIG. 5A illustrates a side view of an integrated circuit assemblyaccording to one embodiment of the invention.

FIG. 5B illustrates another side view of an integrated circuit assemblyaccording to one embodiment of the invention.

DETAILED DESCRIPTION

In the following detailed description of the invention reference is madeto the accompanying drawings which form a part hereof, and in which areshown, by way of illustration, specific embodiments in which theinvention may be practiced. In the drawings, like numerals describesubstantially similar components throughout the several views. Theseembodiments are described in sufficient detail to enable those skilledin the art to practice the invention. Other embodiments may be utilized,and structural, logical, and electrical changes may be made, withoutdeparting from the scope of the present invention. The followingdetailed description is, therefore, not to be taken in a limiting sense,and the scope of the invention should be determined with reference tothe appended claims, along with the full scope of equivalents to whichsuch claims are entitled.

The term “active side” as used in this description is defined as theconventional horizontal, large plane or surface of a chip or die whereelectrical devices have typically been fabricated, regardless of theorientation of the chip or die. The term “back side” as used in thisdescription is defined as a conventional horizontal, large plane orsurface of a chip or die that generally does not contain active deviceson its surface. The term “vertical” refers to a direction perpendicularto the horizontal as defined above. Prepositions, such as “on”,“higher”, “lower”, “above” and “below” are defined with respect to theconventional plane or surface being on the active side of the chip ordie, regardless of the orientation of the chip or die.

An example of an information handling system using processor chips isincluded to show an example of a higher level device application for thepresent invention. FIG. 1 is a block diagram of an information handlingsystem 1 incorporating at least one electronic assembly 4 utilizing athermal interface structure in accordance with at least one embodimentof the invention. Information handling system 1 is merely one example ofan electronic system in which the present invention can be used. In thisexample, information handling system 1 comprises a data processingsystem that includes a system bus 2 to couple the various components ofthe system. System bus 2 provides communications links among the variouscomponents of the information handling system 1 and can be implementedas a single bus, as a combination of busses, or in any other suitablemanner.

Electronic assembly 4 is coupled to system bus 2. Electronic assembly 4can include any circuit or combination of circuits. In one embodiment,electronic assembly 4 includes a processor 6 which can be of any type.As used herein, “processor” means any type of computational circuit,such as but not limited to a microprocessor, a microcontroller, acomplex instruction set computing (CISC) microprocessor, a reducedinstruction set computing (RISC) microprocessor, a very long instructionword (VLIW) microprocessor, a graphics processor, a digital signalprocessor (DSP), or any other type of processor or processing circuit.

Other types of circuits that can be included in electronic assembly 4are a custom circuit, an application-specific integrated circuit (ASIC),or the like, such as, for example, one or more circuits (such as acommunications circuit 7) for use in wireless devices like cellulartelephones, pagers, portable computers, two-way radios, and similarelectronic systems. The IC can perform any other type of function.

Information handling system 1 can also include an external memory 10,which in turn can include one or more memory elements suitable to theparticular application, such as a main memory 12 in the form of randomaccess memory (RAM), one or more hard drives 14, and/or one or moredrives that handle removable media 16 such as floppy diskettes, compactdisks (CD), digital video disk (DVD), and the like. Examples of mainmemory 12 include dynamic random access memory (DRAM), synchronousdynamic random access memory (SDRAM), flash memory, static random accessmemory (SRAM), etc.

Information handling system 1 can also include a display device 8, oneor more speakers 9, and a keyboard and/or controller 20, which caninclude a mouse, trackball, game controller, voice-recognition device,or any other device that permits a system user to input information intoand receive information from the information handling system 1.

Although the present invention is found to be effective at transferringheat from IC surfaces, the invention is not limited to heat transferfrom IC surfaces. The invention can be used in any setting where heat isto be conducted from one surface to another. For ease of explanation,the example of cooling an IC will be used.

FIG. 2A shows a cross-sectional representation of an IC package 200. Inembodiments where the IC die is a processor die, the IC package can betermed a processor assembly. IC package 200 includes an IC die 210mounted in “flip-chip” orientation with its active side facing downwardto couple with an upper surface of a substrate 220, such as a circuitboard, through solder balls or bumps 212. Substrate 220 can be aone-layer board or a multi-layer board, and it can include additionalcontacts 222 on its opposite surface for mating with additionalpackaging structure (not shown).

Die 210 generates its heat from internal structure, including wiringtraces, that is located near its active side; however, a significantportion of the heat is dissipated through its back side 214. Heat thatis concentrated within the die is dissipated to a large surface that isin contact with the die in the form of an integrated heat spreader 230that is typically formed of metal such as copper or aluminum. In oneembodiment, the integrated heat spreader 230 is formed into a partialenclosure, and serves as a package cover for the die 210. In oneembodiment, a sealant 234 is further included to isolate and secure theintegrated heat spreader 230 to the substrate 220. To improve thethermal conductivity between the die 210 and the integrated heatspreader 230, a thermal interface material 240 is often provided betweenthe die 210 and integrated heat spreader 230.

In one embodiment, to further dissipate heat from the integrated heatspreader 230, a heat sink 250 optionally having fins 252 is coupled tothe integrated heat spreader 230. Heat sink 250 dissipates heat into theambient environment. In one embodiment a second thermal interfacematerial 254 is further utilized to create a thermal pathway between theintegrated heat spreader 230 and the heat sink 250.

The thermal interface material 240 shown in FIG. 2A is intended to be ageneral illustration of a thermal interface material or thermalinterface structure. In the following detailed description, specificdetails of thermal interface structures and assemblies are illustratedfor given embodiments of the invention.

FIG. 2B shows an embodiment of an IC package 200 without an additionalheat sink 250 attached as described above. The integrated heat spreader230 is shown in an embodiment formed as a package cover. The edges ofthe integrated heat spreader 230 form an enclosure with the substrate220 where the die (not shown) is substantially enclosed. In oneembodiment, an opening 232 is included in the integrated heat spreader230. In one embodiment, the opening 232 provides a relief for variationsin pressure due to thermal changes in the die.

FIG. 3A shows a heat conducting assembly 300, including a heat spreader320 and a thermal interface structure 310. In one embodiment, the heatspreader 320 includes an integrated circuit package cover, although theinvention is not so limited. In one embodiment, the heat spreader 320includes an integrated heat spreader. In one embodiment the heatspreader 320 includes the material copper, although other heatconducting materials, such as aluminum or AlSiC are within the scope ofthe invention. In one embodiment, the heat spreader 320 is coated withnickel (Ni) on at least a portion of its exterior surfaces to providedesirable chemical interaction properties, such as with its environment,or other components.

The thermal interface structure 310 of FIG. 3A includes a number ofguide structures 312 and a number of spaces 314. In embodiments thatwill be described below, the number of guide structures 312 and thenumber of spaces 314 are used to conduct a fluid within the thermalinterface structure 310 to enhance thermal conduction within the thermalinterface structure 310. In one embodiment, the number of guidestructures includes a perimeter seal portion that will be described inmore detail in sections below.

In one embodiment, the thermal interface structure 310 includes amaterial that is plastically deformable under certain conditions oftemperature and pressure. An operation such as cold forming causesplastic deformation in materials at temperatures below their meltingpoints. In one embodiment, the thermal interface structure 310 includesa metal. In one embodiment, the thermal interface structure 310 includessolder. Suitable materials for the thermal interface structure 310include, but are not limited to tin (Sn), indium (In), and silver (Ag).Alloys of tin, indium and silver, with each other, or with other metalsare also within the scope of the invention.

FIG. 3A further shows an interface 318 between the thermal interfacestructure 310 and the heat spreader 320. In one embodiment the interface318 is formed at least partially using plastic deformation.

A noted above, in a deformation operation such as cold forming, at leasta portion of the material being forrried deforms plastically. After coldforming the thermal interface structure 310 against the heat spreader320, a number of cold formed features are observed at the interface 318.In one cold formed feature, the deformation causes the deforming portionof the material to flow in a conforming manner into surface features ofthe heat spreader 320. In this way, substantially all gaps present atthe interface 318 are removed as the thermal interface structure 310 isdeformed into surface features on the heat spreader 320.

In one embodiment, a cold formed feature includes a mechanical bond thatis formed at the interface 318 during plastic deformation. In amechanical bond, certain portions of the thermal interface structure 310flow around asperities or surface features of the heat spreader 320.After deformation is complete, the interface 318 is at least partiallyheld together mechanically by the asperities or surface features beingembedded within the flowed portion of the thermal interface structure310. This is in contrast to chemical bonding where actual bonds areformed between atoms of the thermal interface structure 310 and atoms ofthe heat spreader 320. In one embodiment, the interface 318 is roughenedon the heat spreader 320 to enhance a mechanical bond. In oneembodiment, a combination of chemical bonding, such as a formation ofintermetallic compounds, and mechanical bonding are formed at theinterface 318. For example, in embodiments where the heat spreader 320includes a nickel coating, and the thermal interface structure 310includes indium, an intermetallic compound of indium and nickel isformed.

In one embodiment, a cold formed feature includes work hardening of thethermal interface structure 310. The plastic deformation of portions ofthe thermal interface structure 310 acts to raise the hardness andstrength of the thermal interface structure 310.

In one embodiment, the plastic deformation takes place below a meltingtemperature of the material being deformed. Once a material, such as thethermal interface structure 310, is in its liquid state, wetting of theliquid against the other surface, such as the heat spreader 320 becomesan issue. Due to chemical incompatibility, the liquid thermal interfacestructure 310 may not wet well against the heat spreader 320. In suchcircumstances, undesirable voids will form at the interface 318. Thevoids are undesirable because they do not conduct heat effectively, andthey provide less effective mechanical strength at the interface 318. Bymaintaining the temperature below a melting temperature of the thermalinterface structure 310, issues of wetting at the interface 318 areavoided.

In one embodiment, the plastic deformation takes place above ambienttemperatures. As temperature increases, the strength of the thermalinterface structure 310 decreases. In this way, the force necessary tocause plastic deformation can be adjusted by varying the temperature. Bymaintaining the temperature above ambient temperatures, plasticdeformation is accomplished with lower forces, and the thermal interfacestructure 310 flows better into surface features of the heat spreader320 with advantages such as better interface contact, and highermechanical strength as discussed above. In one embodiment, the plasticdeformation takes place at a temperature between approximately 130° C.and 145° C. In one embodiment, a load of approximately 20–100 pounds isused in the plastic deformation operation. In one embodiment, conditionssuch as temperature and load are sustained for approximately one minuteduring the plastic deformation operation. In embodiments usingsubstantially pure indium, processing conditions of pressure andtemperature are suited to plastic deformation without damage to otherstructures such as integrated circuit chips.

FIG. 3B shows a chip assembly 302 further including an integratedcircuit chip 330. In one embodiment, the integrated circuit chip 330includes a processor chip. A backside 332 of the integrated circuit chip330 and an active side 334 of the integrated circuit chip 330 arefurther shown in FIG. 3B. In one embodiment, the integrated circuit chip330 is mounted in flip-chip orientation, with the active side 334 up asillustrated in FIG. 3B.

In one embodiment, the thermal interface structure 310 is attached tothe heat spreader 320 using methods described above prior to attachingthe thermal interface structure 310 to the integrated circuit chip 330.In one embodiment, the thermal interface structure 310 is attached tothe integrated circuit chip 330 using methods described above prior toattaching the thermal interface structure 310 to the heat spreader 320.In one embodiment, the thermal interface structure 310 is attachedconcurrently using methods described above to both the heat spreader 320and the integrated circuit chip 330. Accordingly, selected embodimentsinclude one or more interfaces of the thermal interface structure 310(such as interface 318, or the opposite interface at the backside 332 ofthe integrated circuit chip 330) with cold formed features.

FIG. 3C shows a processor assembly 304. The heat spreader 320 is shownwith the thermal interface structure 310 and a processor chip used asthe integrated circuit chip 330. In the embodiment shown in FIG. 3C, asealant 322 is shown between the heat spreader 320 and a substrate 350.A heat sink 340 is also shown with a number of fins 342. Othercomponents are included in FIG. 3C that are similar to those illustratedin FIG. 2A.

FIG. 3C shows a thickness 316 of the thermal interface structure 310. Inone embodiment, the thickness 316 is in a range of approximately0.0025–0.0050 cm thick. In one embodiment, manufacturing methods such ascold forming at least one interface of the thermal interface structure310 allows a thickness 316 to be reduced to the range of 0.0025–0.0050cm. In one embodiment, the use of manufacturing methods such as coldforming on at least one interface of the thermal interface structure 310allows a reduction in process steps such as formation of intermediateinterface layers.

In selected embodiments, a liquid material is placed within the numberof spaces 314 in the thermal interface structure 310. In one embodiment,the liquid material includes a liquid metal material. In one embodiment,the liquid material includes liquid gallium metal. Gallium metal isliquid at ambient temperatures (around 30° C.), and is a good conductorof heat at approximately 41 W/mK. Other liquid materials aside fromgallium or other liquid metals are acceptable provided they are liquidat appropriate operating temperatures and are effective conductors ofheat. In selected embodiments, during a heat conducting operation, theliquid material is circulated within the thermal interface structure 310to enhance heat spreading and heat dissipation. In one embodiment, awidth 317 of selected spaces in the number of spaces 314 is tailored toadjust the circulation flow. In one embodiment, the width 317 of atleast one of the number of spaces 314 is in a range of approximately0.0025–0.0050 cm.

Embodiments of the thermal interface structure 310 as described aboveprovide a composite heat conducting mode of operation. In oneembodiment, heat is conducted into the liquid material, whileconcurrently heat is conducted into the number of guide structures 312.A composite thermal conductivity of the thermal interface structure 310can therefore be calculated with a contribution from the liquid materialand a contribution from the number of guide structures 312. Oneadvantage of using a metal material to form the number of guidestructures 312 is that the heat conduction contribution from the numberof guide structures 312 is high compared to other materials such aspolymers or ceramics, etc. Indium metal, for example, has a thermalconductivity of approximately 82 W/mK.

In one embodiment, the number of spaces 314 form a direct interface atinterface 318 with the heat spreader 320. In one embodiment, the numberof spaces 314 form a direct interface at backside 332 of the integratedcircuit chip 330. As illustrated in FIG. 3C, in one embodiment, thenumber of spaces 314 form a direct interface at both the interface 318with the heat spreader 320, and at the backside 332 of the integratedcircuit chip 330. A direct interface of the liquid material with theintegrated circuit chip 330 enhances heat conduction into the liquidmaterial from the integrated circuit chip 330 without interveninglayers. Similarly, a direct interface of the liquid material with theheat spreader 320 further enhances conduction of heat within the liquidmaterial out to the heat spreader 320.

FIG. 4 shows a thermal interface cooling assembly 400. The coolingassembly 400 includes a thermal interface structure 410 coupled to aportion of a surface of an integrated circuit chip 430. A section of anintegrated heat spreader 420 is shown surrounding the integrated circuitchip 430 and the thermal interface structure 410. Although the thermalinterface structure 410 shown in FIG. 4 covers only a fraction of thesurface of the integrated circuit chip 430 (such as a high heatgenerating area), other embodiments include a thermal interfacestructure 410 that entirely covers the surface of the integrated circuitchip 430.

The thermal interface structure 410 includes a perimeter seal portion411 and a number of guide portions 412 within an area defined by theperimeter seal portion 411. In one embodiment, the perimeter sealportion 411 functions to retain an amount of liquid within spaces 414 ofthe thermal interface structure 410, between the integrated circuit chip430 and the heat spreader. In one embodiment, the perimeter seal portion411 and the number of guide portions 412 are formed integrally from asingle sheet or portion of base material. Other embodiments may includea seal portion that is formed separately from the number of guideportions 412. In one embodiment, the perimeter seal portion 411 and thenumber of guide portions 412 are formed concurrently using a stamping ordie cutting operation. In one embodiment, the perimeter seal portion 411and the number of guide portions 412 are formed concurrently as a coldformed interface is formed on a surface such as a surface of a heatspreader as described in embodiments above. For example, a stamping diecuts the perimeter seal portion 411, and concurrently provides a loadused to cold form the perimeter seal portion 411.

FIG. 4 further shows a circulation system including a pump 460 and anumber of transmission lines 462. The number of transmission lines 462are coupled to the thermal interface structure 410 at a firstinlet/outlet 464 and a second inlet/outlet 466. In one embodiment, afill port 468 is included to facilitate introduction of the liquidmaterial to the spaces 414 during manufacture of the cooling assembly400. In one embodiment, the fill port 468 includes a valve. In oneembodiment, a heat exchanger 470 is further included. Elements such asthe pump 460 and the heat exchanger 470 are shown in block diagram formin FIG. 4, and specific locations should not be implied. For example, inone embodiment, the heat exchanger 470 is integral with the pump 460.Examples of heat exchangers 470 include fluid reservoirs, devices withfins, etc.

In operation, the thermal interface structure 410 functions to bothspread heat laterally across the surface of the integrated circuit chip430 and to conduct heat away from the integrated circuit chip 430. Heatremoval is accomplished using features such as circulation of the liquidmaterial external to the thermal interface structure 410, and conductionof heat through the thermal interface structure 410 to the heatspreader.

FIG. 5A shows one embodiment of an integrated circuit chip assembly 500.The assembly 500 includes a heat spreader 520, a thermal interfacestructure 510 and an integrated circuit chip 530. Similar to embodimentsabove, the thermal interface structure 510 includes a number of guidestructures 512 and the number of spaces 514. One configuration of aninlet/outlet 516 is shown. In FIG. 5A, the inlet/outlet 516 passesthrough the heat spreader 520 in a direction substantially perpendicularto a main surface of the heat spreader 520.

FIG. 5B shows another embodiment of an integrated circuit chip assembly502. The assembly 502 includes a heat spreader 520, a thermal interfacestructure 510 and an integrated circuit chip 530. In FIG. 5B, aninlet/outlet 518 is shown passing through the heat spreader 520 at aside portion of the heat spreader 520. Although two possibleconfigurations of inlet/outlet structures are shown, the invention isnot so limited. One of ordinary skill in the art, having the benefit ofthe present disclosure will recognize that other possible configurationsof inlet/outlet structures are within the scope of the invention.

CONCLUSION

Devices and methods including thermal interface structures as describedabove include advantages such as improved interfacial strength, andimproved interfacial contact. This in turn leads to improved heatconduction away from hot areas of a chip. Embodiments described abovefurther include advantages of composite thermal conduction andcirculated liquid cooling. Embodiments are shown that require simple,low numbers of manufacturing steps and reduced thermal interfacethickness.

Although specific embodiments have been illustrated and describedherein, it will be appreciated by those of ordinary skill in the artthat any arrangement which is calculated to achieve the same purpose maybe substituted for the specific embodiment shown. This application isintended to cover any adaptations or variations of embodiments describedabove. It is to be understood that the above description is intended tobe illustrative, and not restrictive. Combinations of the aboveembodiments, and other embodiments will be apparent to those of skill inthe art upon reviewing the above description. The scope of the inventionincludes any other applications in which the above structures andfabrication methods are used. The scope of the invention should bedetermined with reference to the appended claims, along with the fullscope of equivalents to which such claims are entitled.

1. An integrated circuit chip assembly, comprising: an integratedcircuit chip; a heat spreader; a thermal interface structure, includinga perimeter seal portion, the seal portion coupled between the heatspreader and at least a portion of a surface of the integrated circuitchip; and wherein at least one interface of the perimeter seal portionincludes cold formed features.
 2. The integrated circuit chip assemblyof claim 1, wherein the thermal interface structure further includes aliquid material located within the perimeter seal portion and betweenthe integrated circuit chip and the heat spreader.
 3. The integratedcircuit chip assembly of claim 2, wherein the liquid material is indirect contact with both the integrated circuit chip and the heatspreader.
 4. The integrated circuit chip assembly of claim 2, whereinthe liquid material includes liquid gallium metal.
 5. The integratedcircuit chip assembly of claim 1, further including a number of guideportions within the perimeter seal portion.
 6. The integrated circuitchip assembly of claim 5, wherein the guide portions form longitudinalspaces having widths of approximately 0.0025–0.0050 cm.
 7. Theintegrated circuit chip assembly of claim 1, wherein the perimeter sealportion is formed from indium.
 8. The integrated circuit chip assemblyof claim 1, wherein at least one interface of the perimeter seal portionfurther includes an intermetallic compound formed from a first andsecond mating material at the interface.
 9. The integrated circuit chipassembly of claim 1, wherein the thermal interface structure has athickness of approximately 0.0025–0.0050 cm.